The numbers on plastic containers, enclosed in a triangular recycling symbol, are more than just recycling information; they are a crucial safety guide for food contact and heating. For microwave use, not all plastics are created equal, and some can pose serious health risks when heated. Chemicals can leach from plastic into your food, especially when exposed to the high temperatures generated by a microwave. This guide will explain which numbers indicate microwave safety and which should be avoided, helping you make safer choices in your kitchen.
The Recycling Code System Explained
The recycling code, or resin identification code, is a standardized system developed by the plastics industry to help categorize different types of plastic polymers. Each number from 1 to 7 represents a specific plastic resin with unique properties, including its melting point and chemical stability. While this system is primarily for sorting plastics during recycling, it serves as a valuable shortcut for determining if a container is suitable for microwave use.
How to find the number
The recycling code is typically found on the bottom of a plastic container. You will see a small triangle with a number inside. Look for this symbol to identify the plastic type before microwaving.
Safe Plastic Numbers for Microwaving
Only a couple of plastic resin codes are generally considered safe for microwave use due to their higher heat resistance and stability. However, the most reliable indicator is always the manufacturer's specific labeling.
Plastic #5: Polypropylene (PP)
Polypropylene, marked with a #5, is widely regarded as the safest plastic for microwave use.
- High Melting Point: It is resistant to high heat, with a melting point of approximately 230°F (110°C).
- Heat & Moisture Resistance: This makes it ideal for food storage and reheating without warping or leaching chemicals.
- BPA-Free: Most PP plastics are naturally BPA-free.
- Common Use: Yogurt containers, microwaveable meal trays, and many reusable food storage containers are made from PP.
Plastic #2: High-Density Polyethylene (HDPE)
High-Density Polyethylene, marked with a #2, is generally considered safe for microwaving under normal conditions.
- Durability: HDPE is a robust and durable plastic often used for milk jugs and food containers.
- Temperature Tolerance: It can withstand temperatures up to 266°F (130°C) before distorting.
- Lower Heat Tolerance than PP: While generally safe, prolonged or intense microwave heat can cause deformation more readily than with PP plastics.
The microwave-safe symbol: The best indicator
The most definitive way to know if a plastic container is safe for the microwave is to look for the specific symbol. This emblem usually consists of a microwave with wavy lines inside or above it, or simply the words "Microwave Safe" printed on the bottom. This symbol means the manufacturer has tested the product and certified it for safe microwave use. Never rely on a plastic number alone if the container is not explicitly labeled as microwave safe.
Unsafe Plastics You Must Avoid
Certain plastic types should never be used in the microwave, as they can warp, melt, and release harmful chemicals into your food.
The dangers of heating plastics
When exposed to heat, certain plastics can break down and release harmful substances, such as bisphenols (like BPA, BPS, and BPF) and phthalates, which are known endocrine disruptors. These chemicals can leach into food, especially fatty foods, and have been linked to potential health issues, including reproductive problems, diabetes, and cardiovascular disease. New research also highlights the significant release of microplastics and nanoplastics during heating.
Plastic #1: Polyethylene Terephthalate (PET or PETE)
Typically used for single-use items like water bottles and takeout containers, PET has a low melting point and is not microwave safe. Heating it can cause warping and chemical leaching.
Plastic #6: Polystyrene (PS)
Commonly known as Styrofoam, Polystyrene has a very low melting point and can deform and release harmful chemicals when heated. This applies to both foam and rigid polystyrene containers.
Plastic #3: Polyvinyl Chloride (PVC)
PVC contains plasticizers like phthalates and should not be used for heating food. Heating can release toxic chemicals, including chlorine gas if it overheats. Common uses include some types of cling film and cooking oil bottles.
Plastic #7: "Other" plastics
This is a catch-all category for various plastics, some of which may contain harmful chemicals like BPA. Unless specifically labeled otherwise, containers with a #7 code should be avoided in the microwave.
How to test a container at home
If you are unsure whether a container is safe, you can perform a simple test. Place the empty container in the microwave with a cup of water next to it. Heat for one minute. If the container feels cool to the touch and only the water is hot, it is likely microwave-safe. If the container becomes hot, it is absorbing microwave energy and should not be used. This test does not, however, guarantee that no chemicals are being leached from the plastic.
Comparison Table: Plastic Numbers and Microwave Safety
| Resin Code | Plastic Type | Microwave Safe? | Common Use Cases |
|---|---|---|---|
| 1 | Polyethylene Terephthalate (PETE) | No | Water bottles, single-use food packaging |
| 2 | High-Density Polyethylene (HDPE) | Generally Safe | Milk jugs, durable food containers |
| 3 | Polyvinyl Chloride (PVC) | No | Cooking oil bottles, some cling film |
| 4 | Low-Density Polyethylene (LDPE) | Not Recommended | Bread bags, plastic wrap |
| 5 | Polypropylene (PP) | Yes, with label | Yogurt tubs, microwave-safe containers |
| 6 | Polystyrene (PS) | No | Styrofoam cups, disposable cutlery |
| 7 | Other (incl. Polycarbonate) | No, unless specified | Mixed plastics, some food containers |
Conclusion
While recycling codes provide a helpful guide, they are not a substitute for explicit microwave-safe labeling. For ultimate safety, always look for the microwave-safe symbol or transfer your food to glass or ceramic dishes before heating. By understanding what number of plastic is microwave safe, you can minimize your exposure to potential toxins and protect your family's health. For additional information on plastics and health, visit this guide from Healthline: What Do the Numbers on Plastic Containers Mean, and Should You Avoid Them?.
